Soil nutrient balance in rice−wheat rotation system in Taizhou City of Jiangsu Province

Objectives The purpose of the study is to evaluate the rice-wheat rotation farmland nutrient balance situation in Taizhou, aimed at promoting the cultivated land quality, providing a theory basis for inhibition of agricultural pollution, and coming up with countermeasures and suggestions for cultivated land quality construction and protection in the future.

Methods The data of fertilizer input and crop yield was from the 20 monitoring sites in Taizhou City from 2012 to 2017, which was part of the Farmland Quality Monitoring Database of Jiangsu Province. The annual and average nutrient input and crop uptake in the main rural areas of Taizhou were calculated and compared. The soil nutrient balance rates were calculated according to the crop removal and input, and proposals were given for the efficient nutrient management in Taizhou.

Results During the monitoring period, the total nitrogen input was generally stable, the total phosphorus and potassium fertilizer input were gradually increasing, and a sharp increase in potassium input happened in 2017. The average yield in Taizhou was 4705.5 kg/hm² for wheat grain, 5220.3 kg/hm² for wheat straw, 7049.2 kg/hm² for rice grain and 7511.5 kg/hm² for rice straw. There was neither significant yearly difference in crop yields, nor significant difference among the rural areas. The soil nitrogen and phosphorous were surplus, and potassium was in deficit. The average nitrogen surplus rate was 117.53%, that of phosphorus was 24.19%, and the average potassium deficit rate was −49.04%. The nitrogen surplus rates kept stable, with no significant yearly differences. The phosphorus surplus rates raised slowly every year, with no significant changes. The potassium deficit rate decreased every year, the deficit rate in 2017 was significantly lower than other years, which was −36.19%. The nutrient balance of all rural areas was in accordance with the average situation, nitrogen and phosphorous were in surplus, and potassium in deficit. The nitrogen surplus rate in Lixiahe area was significantly higher than Gaoshatu area (106.27%) and Yanjiang area (106.71%), which was 139.53%. The surplus rate of phosphorus did not show significant differences among the three areas. Gaoshatu area had the lowest annual potassium deficit rate (−40.96%), which was significantly lower than the Lixiahe area (−57.73%) and Yanjiang area (−48.19%).

Conclusions The fertilization use in Taizhou has obeyed the principle of ‘Reducing nitrogen, stabilizing phosphorus and increasing potassium’ for guarantying the stable and high production of crop. As the nutrient surplus and deficit vary in rural areas, specific fertilization measurements should be carried out according to the practical nutrient status in each area of Taizhou.